Leptomitus lineatus

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The tallest sponge from the Burgess Shale

Leptomitus undulatus (ROM 53571) – Holotype (part and counterpart). Only known specimen of this species showing partial base, prominent ridges and top part (osculum). Specimen height = 78 mm. Specimen wet – direct light. Walcott Quarry.

Leptomitus lineatus (USNM 66448) – Lectotype. The tallest and most complete specimen of the species described so far, showing the rounded base and tufted top (left and middle) and detailed sections showing the characteristic arrangement of spicules (right). Specimen height = 360 mm. Specimen dry – direct light (left and top right); dry – polarized light (middle); wet – polarized light (bottom right). Walcott Quarry.

Taxonomy:

Kingdom: Animalia

Phylum: Porifera

Higher Taxonomic assignment: Demospongea (Order: Monaxonida)

Species name: Leptomitus lineatus

Remarks:

Leptomitus is considered a primitive demosponge (Rigby, 1986). Demosponges, the same group that are harvested as bath sponges, represent the largest class of sponges today.

Described by: Walcott

Description date: 1920

Etymology:

Leptomitus – from the Greek lept, “slender,” and mitos, “thread.” This name refers to the overall shape of the sponge.

lineatus – from the Latin lineatus, “streaked.” This refers to the wrinkle appearance of this sponge.

Type Specimens: Lectotype –USNM66448 (L. lineatus) in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA. Holotype –ROM53558 (L. undulatus) in the Royal Ontario Museum, Toronto, Canada.

Other species:

Burgess Shale and vicinity: L. undulatus Rigby and Collins 2004 from the Walcott Quarry.

Other deposits: L. zitteli Walcott, 1886 from the Middle Cambrian Parker Slate in Vermont; L. metta Rigby, 1983 from the Middle Cambrian Marjum Formation of Utah; L. conicus García-Bellido et al., 2007 from the Middle Cambrian Murero Formation of Spain; L. teretiusculus Chen, Hou and Lu, 1989 from the Lower Cambrian Chengjiang biota in China (see Rigby and Hou, 1995); unidentified species from the Lower Cambrian Niutitang Formation in China (Yang et al., 2003).

Age & Localities:

Age:

Middle Cambrian, Glossopleura Zone to Bathyuriscus-Elrathina Zone (approximately 505 million years ago).

Principal localities:

The Walcott Quarry on Fossil Ridge. The Tulip Beds (S7) and the Collins Quarry on Mount Stephen.

History of Research:

Brief history of research:

Leptomitus was originally described by Charles Walcott (1920) as a new genus “Tuponia” along with several species (T. lineatea, T. flexilis, T. flexilis var. intermedia). This genus was later synonymized by Resser and Howell (1938) with Leptomitus, a genus named by Walcott in 1886. Ribgy (1986) redescribed the Burgess Shale sponges including Leptomitus and considered L. flexilis to be a junior synonym of L. lineatus. Rigby and Collins (2004) added a second species L. undulatus based on new material collected by the Royal Ontario Museum.

Description:

Morphology:

L. lineatus is an elongate tubular sponge with a double-layered skeleton. The outer layer is composed of long monoaxial spicules (simple spicules with pointed ends) arranged vertically along the length of the sponge. The varying thicknesses of these elongate spicules give the sponge a distinctive wrinkly appearance in the fossils. The inner layer is composed of tiny horizontal spicules that form an unclumped thatch; these tufts can be seen at the oscular margin (opening at the top of the sponge). The base of the sponge is rounded in shape and would have had a small holdfast structure. L. undulatus has the same wall structure as L. lineatus but has a rounder goblet shaped skeleton.

Abundance:

L. lineatus is relatively common in the Walcott Quarry and represents 0.26% of the community (Caron and Jackson, 2008). L. undulatus is known from a single specimen.

Maximum Size:

360 mm

Ecology:

Life habits: Epibenthic, Sessile

Feeding strategies: Suspension feeder

Ecological Interpretations:

Leptomitus would have lived attached to the sea floor. Particles of organic matter were extracted from the water as they passed through canals in the sponge’s wall.

References:

CARON, J.-B. AND D. A. JACKSON. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

CHEN, J. Y., X. G. HOU AND H. Z. LU. 1989. Lower Cambrian leptomitids (Demospongea), Chengjiang, Yunnan. Acta Palaeontologica Sinica, 28: 17-31.

GARCÍA-BELLIDO, D. C., R. GOZALO, J. B. CHIRIVELLA MARTORELL AND E. LIÑÁN. 2007. The demosponge genus Leptomitus and a new species from the Middle Cambrian of Spain. . Palaeontology, 50: 467-478.

RESSER, C. F. AND B. F. HOWELL. 1938. Lower Cambrian Olenellus Zone of the Appalachians. Geological Society of American Bulletin, 49: 195-248.

RIGBY, J. K. 1983. Sponges of the Middle Cambrian Marjum Limestone from the House Range and Drum Mountains of Western Millard County, Utah. Journal of Paleontology, 57: 240-270.

RIGBY, J. K. 1986. Sponges of the Burgess shale (Middle Cambrian), British Columbia. Palaeontographica Canadiana, 2: 105 p.

RIGBY, J. K. AND D. COLLINS. 2004. Sponges of the Middle Cambrian Burgess Shale and Stephen Formations, British Columbia. Royal Ontario Museum Contributions in Science (1): 155 p.

YANG, R., W. ZHANG, L. JIANG AND H. GAO. 2003. Chengjiang biota from the Lower Cambrian Niutitang Formation, Zunyi County, Guizhou Province, China. Acta Palaeontologica Sinica, 77: 145-150.

WALCOTT, C. 1886. Second contribution to the studies on the Cambrian faunas of North America. U.S. Geological Survey Bulletin, 30: 1-369.

WALCOTT, C. D. 1920. Middle Cambrian Spongiae. Cambrian Geology and Paleontology IV. Smithsonian Miscellaneous Collections, 67(6): 261-365.